While often we think of student feedback in terms of official evaluation forms like (at Harvard) the Q Guide, in fact we as instructors have the option of soliciting an almost constant stream of feedback from students through low-stakes exercises and relatively informal interactions in class and/or in office hours. Much of this feedback requires little or no effort to collect: we can learn a lot simply by slowing down a bit and taking the time to "read" our students in class. Registering our students' attention spans, scanning for looks of confusion, pausing to ask for questions, or requesting that a volunteer summarize or apply a concept we've just taught are all easy ways to get a quick read on how well our students understand what we are teaching in real time.
There are other, more formal ways of collecting such ongoing feedback; even these, however, require only a modest amount of effort. Some can be done outside of the regular class period, like scheduling brief office hours appointments with students either before or after an assignment is due. (This can be an excellent way not only to offer your students feedback on their work, but also to give them the chance to raise any concerns which they have about their progress in the class.) Within the regular class period, many instructors collect feedback through one of a number of low-stakes, anonymous exercises known in the field as Classroom Assessment Techniques (CATs). Among the best-known of these are "minute papers," in which students jot down a metacognitive reflection on their learning in response to questions like "What was the most important thing you learned during this class?" or "What do you still not understand?", or "the muddiest point," in which students journal briefly on a concept that remains most confusing or unclear to them.
Finally, there is always the option of polling software like PollEverywhere (for which students can use their laptop, tablet, or computer) or Learning Catalytics (which requires the use of clickers). Through these technologies, instructors can poll students in real time, either to check their comprehension (through multiple choice) or to prompt group brainstorming. It can be particularly effective to use polling software to show students how their own attitudes and understandings are changing over the course of one or more class periods, by asking students the same question at the end of a unit of instruction as at the start. How many students have changed their mind or understood an issue or concept differently after completing the unit?